Analglyphic representations of image and elevation data

ABSTRACT

An anaglyph of an image, the anaglyph comprising a plurality of a anaglyph pixels, each of the anaglyph pixels having an intensity of a first hue and an intensity of an orthogonal second hue wherein when viewed with apparatus which admits the first hue only to a viewer&#39;s right eye and admits the second hue only to the viewer&#39;s left eye, the image is perceived to be three-dimensional with each pixel in the image projected from an associate vantage point unique to such pixel.

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed of U.S. provisional patent application No.60/092,069, entitled “Process for Producing and Product Composed ofAnaglyphic Representations of Image and Elevation Data” filed Jul. 8,1998.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to the fields of digital image processing andmore particularly to the creation and presentation of three-dimensional(3-D) images on a two dimensional viewing surface.

(2) Description of the Related Art

Since the invention of the stereoscope in the mid 1800s, there have beenmany successful attempts to make full use of human binocular vision'sability to combine two separate images, one each obtained by each eyeviewing the same scene from slightly different angles, into one imagewhich is perceived as having depth. The mechanics by which the humanbrain combines two flat images into one image producing the sensation ofa three dimensional world is not fully understood. However, manytechniques have been developed which deliver, by way of differingprocesses, slightly different two dimensional images to each eye so asto produce in the brain a perception indistinguishable from thatobtained by actually viewing the three dimensional world. Thesetechniques belong generally to two major classes, specifically theautostereoscopic imaging class which produces 3-D images viewable by theunaided eye, and the binocular stereoscopic imaging class which produces3-D images requiring observers to wear spectacles or viewers. Techniquesof the later class can be found in 3-D movies of the 1950s and in recentimages returned from the surface of Mars.

Early stereoscopes commonly utilized a specialized device into which wasinserted an image comprised of two nearly identical but separate imagesreproduced side-by-side. Each separate image was created byphotographing a scene from one of two slightly different angles. Whenviewed through the stereoscope, each eye was constrained so as to seeonly one of the images and the perception of three dimensions wasachieved. While this sort of stereoscope does allow for each separateimage to be viewed in color and with minimal distortion of the originalscene, it possesses the drawback of requiring apparatus to properlyconstrain each eye's field of vision and, by so doing, the ability ofthe viewer to move closer or further, up or down, right or left aboutthe image is severely restricted. Anaglyphs, while generally restrictingthe creation of 3-D images to those comprised of varying shades of gray,provide the advantage of requiring less obtrusive apparatus for viewing,consist of only one image to be viewed as opposed to two images placedside by side, and allow the viewer to move freely about the image.

An anaglyph is defined as a composite picture printed in two colors thatproduces a three-dimensional image when viewed through spectacles havinglenses of corresponding colors. The best results are obtained when thecolors (or, more precisely, hues) used to produce the anaglyph representorthogonal hues. That is to say, a change in the intensity of one of thehues present at any point on the image does not affect the intensity ofthe other hue. One typical choice of hues used to produce anaglyphs isthat of red and cyan. When a red image is combined with a slightlydifferent cyan image and viewed through glasses having one lensfiltering out all but the cyan light and the other lens filtering outall but the red light, the perception of 3-D is accomplished. Becausethe filters allow only light of one particular wavelength to passthrough, the anaglyph is effectively split into two images with each eyeseeing a scene depicting the original scene as viewed from one of twoslightly different angles.

Barring occlusion, each picture element (hereinafter “pixel”) isrepresented twice in the anaglyph, once in cyan and once in red. Thehorizontal distance separating the two pixels of differing hue, each ofwhich represents the same pixel in the original image, determines theextent to which the pixel appears in front of or behind the image plane.The “image plane” is defined as the plane containing the paper or othermedium upon which the anaglyph is displayed. A pixel which rests inthree dimensions upon the image plane is unique in that both its red andcyan representations occur at the exact same spot on the anaglyph and,hence, appear to rest in three dimensions upon the image plane. Thegreater the distance separating the red and cyan representations of apixel in an anaglyph, the greater the distance the pixel appears to restin 3-D either above or below the image plane.

Historically, the most common method of producing both stereograms andanaglyphs has been photographic in nature. In such instances, theseparate images used to comprise the stereogram or anaglyph are capturedphotographically. Early 3-D stereograms of cityscapes and anaglyphicmovies were created by utilizing two cameras separated by a distance,aimed in the same direction, and operated simultaneously. More recently,satellite images have been used to form stereograms. For instance,stereograms have been assembled from images in the overlap region of twogeostationary satellites. With the proliferation of computer technology,it is now possible to describe mathematically, in a computer, objectswhich need not exist in the natural world, generate realistic twodimensional views from slightly different angles, and combine the viewsto form stereograms and anaglyphs.

While creation of 3-D images on a computer allows for complete controlover the components of the final image, computer-generated 3-D imagesrequire considerably more expertise and information to create than dotheir photographic forbears. One need simply open one's eyes or pointtwo cameras in any direction to obtain two scenes from slightlydifferent angles. It is not necessary for the perception of depth toacquire a detailed mathematical description of any one object's relativedistance let alone the exact positioning in three dimensions of everysingle point, comprising every single surface, of every single objectwhich is visible to the observer. In contrast, the creation of acomputer generated stereogram or anaglyph does require such detailedinformation.

While photographic and computer generated anaglyphs differ in the mannerby which they are created, the results obtained by either method arequite similar in many important respects. Most importantly, both methodsseek to provide each of the viewer's eyes with a scene that issubstantially similar to that which would be observed were the observerto look with unaided vision from a particular vantage point at hissurroundings. Photographic anaglyphs produce the sensation of viewing athree dimensional landscape from the vantage point at which the cameraswere situated. Computer generated anaglyphs, while able to choose anyhypothetical vantage point from which to create the necessary images,must choose only one vantage point.

The restriction imposed by choosing one vantage point imposes bothadvantages and disadvantages. One primary advantage is that theperception of a three dimensional scene is virtually free of distortion.By mimicking that which the unaided eye would normally observe, theanaglyph produces a sensation quite similar to that produced by naturalbinocular vision. As discussed, early stereoscopes were comprised ofapparatus which constrained the motion of the observer around the image.Early 3-D anaglyphic movies required all observers to be seated somedistance from the screen and hence constrained all viewers to a viewingangle approximately perpendicular to the image plane. While producing aquite realistic three dimensional sensation, such applications of 3-Dtechnology have remained interesting gimmicks with little wide spreadapplication.

One primary reason for the limited application of anaglyph technologyhas been the general requirement that the 3-D image be viewed from asingle point approximating the location from which the anaglyph wasphotographed or from which it was computed. The sensation of 3-Dproduced when viewing the real world is most pronounced when objects areviewed from a relatively small distance. When viewing far away hills, oreven the far side of a room, the brain relies much more on visual cuessuch as shading, texture, and occlusion to interpret depth information.This reliance on visual cues, separate from that which is strictlybinocular in nature, is the result of variations in viewing angles. Forexample, the amount that each eye must deflect from a parallelorientation fixed on infinity to view a spoon held mere inches fromone's face is quite severe. In addition, the difference between such anangle of deflection and one produced when viewing the same spoon held atarm's length is likewise quite large. Contrast this with difference inangle existing when viewing a hill that is one mile away and a starwhich is several hundred million miles away. In the latter instance, therelative difference in viewing angles is quite slight.

Therefore, anaglyphs produced from a single vantage point enjoy theirgreatest utility when presenting objects that are relatively close tothe observer. Unfortunately, such anaglyphs are constrained to arelatively small field of view. Were one to stare off center or at theperiphery of an anaglyph, as opposed to a viewing angle perpendicular tothe image plane, the image appears greatly distorted. Therefore, anunfortunate paradox arises. Anaglyphs of far away objects allow for agreater field of view and appear less distorted when viewed fromslightly different angles but the 3-D effect is diminished from theoutset owing to the large distance between the objects and the viewer.Conversely, objects close to the viewer appear in very realistic 3-D butthe field of view is diminished greatly and even slight movements aboutthe anaglyph result in large distortions.

One subset of three dimensional objects that in theory would benefitmost from the advantages of traditional anaglyph technology whilesuffering most from its disadvantages is the set consisting of planetarysurfaces. Traditionally, such surfaces have been portrayed in twodimensions in the familiar guise of maps. In addition, planetarysurfaces have for some time been recreated in true three dimensionalform as globes, but suffer from problems related to the inability tostore, reproduce, transmit, and conveniently bundle a spherical objectin the same manner as one can a flat image. Furthermore, as theEncyclopedia Americana observes, “The spherical surface of a globecannot be flattened into a map without stretching or tearing; therefore,distortion occurs in the process.” This simple premise, long consideredto be an unavoidable fact, has given rise to myriad map projections overthe millennia. Map projections such as the mercator, plate carée, andothers all seek to derive maximum utility when displaying map data whileminimizing the inevitable distortion.

While different projections address differently the problems oflongitudinal and latitudinal distortion, they do not generally make anyattempt to incorporate elevation data. Much as the human eye can gatherdepth information from visual cues, many maps incorporate colors, shadedrelief, and contour lines of equal elevation to transmit courseelevation data. Shaded relief illustrates the roughness of terrain andchanges in elevation but cannot show actual elevation. Contour lines canshow the horizontal shape of vertical features and the elevation valuesof the quantized contour lines, but do not show the actual verticalshape. However, to see the actual shape of a planetary surface, somemethod of displaying the surface in true 3-D is required.

The related art in anaglyph production allows one to overcome theproblems of distortion associated with flattening a spherical globe ontoa two dimensional map. It is quite possible to compute two slightlydifferent views of a spherical surface as they would appear to anunaided observer. However, such an anaglyph, while accuratelyrepresenting the three dimensional surface of a planet with little or nodistortion, would be of relatively less use as a map. As discussed, oneprimary drawback of a traditional anaglyph is the necessity of viewingthe final image from one and only one vantage point, the point in spacefrom which the original images were photographed or computed. Maps arecustomarily viewed from a variety of vantage points. Large scalepolitical maps may be viewed from a greater distance so as to observerelatively large land masses, boundaries, and the interplay of point,line, and area data. Before battle, Napoleon customarily placed his mapson the floor, alternatingly standing above them and crawling over them.Were a traditional anaglyph used to produce a map in accordance with therelated art, such movement by the observer would be impossible. Becausethe map would be projected and computed as seen from a singular vantagepoint, movement by the viewer away from the intended viewing point inspace would cause gross distortion.

A partial solution to these problems prevalent in the anaglyphic displayof map data was revealed in an article by W. Pichel [Bulletin of theAmerican Meteorological Society, Vol. 54, No. 7, July 1973, pp.688-691]. Pichel created an algorithm for creating stereo pair imagesfrom satellite images one of which was comprised of the visiblespectrum, the other containing infrared (IR) data. On a line-by-linebasis, the IR data was used as a pseudo height indicator for eachcorresponding pixel in the visible image. As Pichel explained:

Thus a simple computer algorithm treats coincident scan lines of visualchannel data and the equivalent IR data that have been transformed intoa scan profile of height levels. The output is a visual channel stereoline pair in which the visual data are displayed with no change inposition for elements at zero height level, but in which elements atother levels are shifted in position. A picture element with heightlevel “h” is displaced from its original position by “h” spots to theright in the left stereo view and “h” spots to the left in the rightstereo view . . .

A dilemma is encountered where two picture elements are competing forthe same location. At present the higher element is retained and thelower element is discarded. In other instances gaps may exist after thedisplacement process is completed.

While producing pleasing images which, if georeferenced, could beconsidered as maps, this methodology suffers from four drawbacks. First,elevations appear relatively correct but absolutely incorrect. Clouds oflower temperature, and hence higher elevation, will appear moredisplaced than clouds of higher temperature and will thus appear to beat a higher elevation everywhere on the map. However, the apparentdifference in elevation between a pixel at level five and a pixel atlevel ten will not appear to be the same difference in elevation asbetween a pixel at level ten and a pixel at level fifteen. In each case,the difference in elevation is five units but the simple algorithm ofpixel displacement employed produces nonlinear viewing effects. Thisconcern is minimized when one considers that the underlying elevationdata is itself not considered to be absolutely correct as therelationship between elevation and temperature in the atmosphere is notperfectly linear. Therefore, the elevation levels computed were acceptedas rough estimates from the outset.

Second, the creation of a stereogram produces two images side by side.As such, the same pixel appearing in each image is separated on averageby the approximate width of either image. Therefore, either with specialviewing apparatus or without, the ability of the observer to move aroundthe image is curtailed. Third, this simple algorithm, by displacing allof the pixels in either computed image either all to the left or all tothe right, features appear either uniformly in front of or behind theimage plane. Thus, a map computed using this algorithm could not haveboth mountains rising from the image plane and canyons descendingbeneath it. The entire surface would have to appear either entirelybelow or entirely above the image plane.

The fourth and most difficult problem to overcome is the likely presenceof gaps resulting from the displacement process. The simplest algorithmsfor reprojecting image data involve mapping each pixel on the originalimage to a location on the final image. A simple forward lookingalgorithm such as the one presented above possesses the attribute ofbeing very simple and fast to implement. Unfortunately, because severalpixels in the original image may map to the same location in the finalimage, there are likely to exist gaps in the final image consisting ofpixel locations onto which no pixels were mapped. In such cases,smoothing algorithms can be employed which produce values for themissing pixels while masking the loss of data that produced the problem.The alternative, constructing a process hereby every pixel in the finalimage is assigned a value ascertained by working backwards t o determinewhich pixel at what elevation in the original image would ultimatelyappear to exist at the location being considered, can be prohibitivelycostly in terms of both complexity and computing speed.

Interestingly, in such a process, each pixel is projected in accordancewith its own unique vantage point. Thus, instead of using a singlevantage point for the entire image, there exist as many vantage pointsas there are pixel s in the original image. As mentioned, one advantageof having a single vantage point for viewing a stereoscopic oranaglyphic image is that, when viewed from that point, there isvirtually no distortion present over the entire image. Following themethod described above, displacement of each pixel is computed withoutany regard to a single vantage point governing the projection of theimage as a whole. Such a method possesses unique properties whenemployed to render maps.

A single point represented by horizontally displaced red and cyan pointscomputed and viewed from directly above will not produce eitherlatitudinal or longitudinal distortion. Any distortion present mustarise from the difference between the angle at which the observer viewsthe red and cyan and pixels and nadir. Therefore, pixels appearingimmediately horizontally or vertically adjacent to the point directly infront of the observer will appear slightly distorted. Distortionincreases as the observer's gaze extends radially from nadir. Becausedistortion is directly proportional to the radial aperture of the areabeing viewed by the observer, relatively small areas will appear to bevirtually free of distortion. In order to view larger areas, theobserver must move backwards to increase the field of view. In so doing,the maximum angular distortion present in the larger field of view isreduced to a threshold approximating that of the smaller area viewedfrom a closer vantage point. This results from the fact that viewing alarger area from the same distance as a smaller area requires a greaterdeflection of the viewing angle. However, the angle of deflection isproportional to the viewing distance and thus the viewer may move back,decreasing the deflection of the viewing angle to that experiencedcloser in.

BRIEF SUMMARY OF THE INVENTION

The present invention seeks to maximize the utility derived fromprojecting map data using multiple vantage points while minimizing oreliminating the obstacles present in the related art. As mentioned,traditional anaglyphic techniques utilizing one vantage point permitviewing of the image from one point with virtually no distortion, butresult in large amounts of distortion when the viewer moves evenslightly around the image. The present invention projects each pixelindividually. One notable difference between the present invention andthe related art is that while each pixel is projected from a differentvantage point, each pixel is projected as though viewed from directlyabove by an observer who is everywhere located the same distance abovethe image and whose eyes are separated everywhere by the same distance.The related art, by virtue of its simple, non-linear computation ofdisplacement, and hence perceived elevation, computed each point ahaving either a different viewing distance, a different eye separation,or both with the result that the vertical scale is not everywhereconstant.

The advantages of such a projection used to produce 3-D maps are many.The most evident advantage is the ability of the viewer to move up anddown, backwards and forwards, and right and left about the map withoutthe perception of overwhelming distortion. Because the map appearsdistortion free from no one place but, rather, contains very littledistortion everywhere, when areas are viewed from a distanceproportional to their size, the map may be scrutinized anywhere on itssurface from up close or from a distance without the introduction ofappreciable distortion. In addition, the vertical exaggeration appearsas “self scaling.” For example, if the vertical exaggeration is computedto be three times that of actual when viewed at a distance of twelveinches, the vertical exaggeration appears to be six times that of theoriginal when viewed at a distance of twenty-four inches. Therefore,vertical exaggeration is made more pronounced, and hence morenoticeable, when the viewer moves further away. Likewise, verticalexaggeration is made less pronounced as the viewer moves in toscrutinize a small area. Such scaling is necessary in the later case toavoid eye strain.

The present invention used for determining the displacement distance ofthe red and cyan pixels, while computationally complex, produces animage in which perceived pixel elevations are both relatively andabsolutely correct. By incorporating the image to be projected into 3-Dwith a digital elevation model (DEM) which contains or from which can becomputed the actual elevation of each pixel in the image, the resultingimage accurately represents each pixel at its correct elevation in 3-D.For example, the perception of a mountain rising 1000 meters from theimage plane would appear to rise a height equal in elevation to thedepth that a canyon cutting 1000 meters into the image plane wouldappear to descend. As is clear from this example, the present invention,by incorporating a more sophisticated projection algorithm than theprior art, allows for the rendering in the same 3-D image of featureswhich both rise above the image plane, and which descend below it.

In addition, the present invention makes use of a computationallyintensive algorithm for determining the location of each red and cyanpixel in the final anaglyph. As mentioned, forward looking algorithms,while simple to implement, often leave gaps in the final imagerepresenting losses of data which must be filled. The present inventioncomputes both the red and cyan finished images by considering each pixelin the final images and working backwards to determine which pixel inthe original image, draped over the corresponding DEM, and viewed fromthe appropriate vantage point, would appear as resting at the finallocation being considered. While considerably more difficult toimplement than a forward looking algorithm, the results produced by thepresent method result in a finished image free from data loss and whichdo not require smoothing.

In addition, the related art gives no indication of a desire or anability to produce a composite anaglyph consisting of different imageseach with a unique DEM. The current implementation allows finishedanaglyphs to be combined with additional point, line, area, or imagedata plotted in varying intensities and constructed from DEMs differingfrom that of the main image. This ability allows one, for instance, todisplay mountains in 3-D while making visible, below a planet's surface,the layout of subterranean coal mines. Similarly, flight paths can bedisplayed in 3-D overlaid atop the terrain over which the plane willtravel. An additional benefit of computing anaglyphs from image and DEMdata, as opposed to. the traditional photographic method, is the abilityto digitally master the images used to create the anaglyph. For example,digital data such as the contours of geological rock strata may beoverlaid on top of satellite data and presented in true 3-D. Theresultant anaglyph allows the viewer to vividly perceive the differentangles at which rock strata rest and interact with geologic forces.

The present invention is not limited to map data. Each data element of amap occupies a unique position in two dimensions as specified by itslatitude and longitude attributes. In addition, the corresponding DEM iscomprised of elevations representing deviations from a point of zeroelevation (which on earth is usually chosen to be sea level). However,the present invention can be applied to any image each pixel of whichpossesses a unique position in two dimensions. For example, the x and yimage pixel locations of each pixel comprising a CAT scan could becombined with elevation data corresponding to the y displacement of eachpixel from a chosen baseline to produce a 3-D image of a body structure.

In addition, the present invention is not limited to an anaglyphic modeof presentation. Left and right views of a full color image may becomputed using the algorithm of the present invention and displayed inalternating and near simultaneous fashion to opposing eyes so as toproduce the sensation of binocular tree-dimensionality.

Accordingly, one aspect of the invention is directed to a method ofcombining digital image data with digital elevation data to produce twoseparate images said separate images, when viewed one with the left eyeand the other with the right eye, producing the sensation of binocularthree-dimensionality, comprising the steps of:

(a) combining said digital image data with said digital elevation datato create a right eye view image with each pixel in said right eye viewimage corresponding to the pixel in said digital image data which wouldappear in three dimensions to reside at the location of said right eyeview image pixel were each of said digital image data pixels to resideupon the surface defined by said digital elevation data, observedindividually directly from above, from a uniform height and eyeseparation, projected upon a plane of uniform height;

(b) combining said digital image data with said digital elevation datato create a left eye view image with each pixel in said left eye viewimage corresponding to the pixel in said digital image data which wouldappear in three dimensions to reside at the location of said left eyeview image pixel were each of said digital image data pixels to resideupon the surface defined by said digital elevation data, observedindividually directly from above, from said uniform height and eyeseparation, and projected upon said plane of uniform height; and

(c) displaying said left eye view image and said right eye view image soas to produce the sensation of binocular three-dimensionality.

Another aspect of the invention is directed to the aforementioned methodwherein said left eye view image and said right eye view image are noteach comprised of a representation of each individual pixel present insaid digital image data arising from the effects of occlusion of saidpixels when said digital image data is viewed in combination with saiddigital elevation data.

Yet another aspect of the invention is directed to the aforementionedmethod wherein the digital image data is preprocessed into a gray imageeach pixel of which contains equal amounts of red, blue and green, saidgray image being subsequently combined with said digital elevation tocreate and display said left eye view image and said right eye viewimage.

Still another aspect of the invention is directed to the aforementionedmethod wherein an anaglyph is formed from said left eye view image andsaid right eye view image comprising the steps of:

(a) assigning each pixel in said left eye view image a single hue;

(b) assigning each pixel in said right eye view image a single hue whichis orthogonal to said single hue assigned to each pixel in said left eyeview image; and

(c) assigning each pixel in said anaglyph the sum of the red, blue, andgreen values present in each corresponding pixel from both the left eyeview image and the right eye view image.

Yet another aspect of the invention is directed to the aforementionedmethod wherein said single orthogonal hues consist of the pairs red andcyan, green and blue, and red and blue..

Yet another aspect of the invention is directed to the aforementionedmethod wherein said left eye view images and said right eye view imagesare displayed on a surface in a manner comprising the steps of:

(a) displaying said left eye view image on the surface in a manner so asto be perceivable by only the viewer's left eye;

(b) displaying said right eye view image on the surface in rapidsuccession with (a) in a manner so as to be perceivable by only theviewer's right eye; and

(c) continuously repeating in an alternating fashion steps (a) and (b).

Another aspect of the invention is directed to the aforementioned methodwherein each of said left eye view images is comprised of multipleseparate left eye view images and each of said right eye view images iscomprised of multiple separate right eye view images combined in amanner comprising the steps of:

(a) computing multiple separate said left and right eye view images eachcovering an area which intersects in whole or in part with that of atleast one other separate said left or right view image;

(b) assigning a multiplier between 0 and 1 to each separate said left orright eye view image corresponding to the desired opacity of eachseparate said view image;

(c) applying the corresponding multiplier to each pixel of each of saidseparate view images; and

(d) adding each corresponding pixel value from each separate left orright view image to form one each of final said left and right eye viewimages.

Yet another aspect of the invention is directed to the immediatelypreceding aspect wherein each of said left and right view images areperceived as consisting of multiple layers of three-dimensional images,each of said layers being partially, fully, or not at all transparentwith respect to other said layers of three-dimensional images.

Yet another aspect of the invention is directed to the aforementionedmethod wherein each row of the right eye view image is created byprojecting a single row of said digital image data in conjunction with asingle row of said digital elevation data while proceeding from left toright across said row of digital elevation data.

Yet another aspect of the invention is directed to the aforementionedmethod wherein each row of the left eye view image is created byprojecting a single row of said digital image data in conjunction with asingle row of said digital elevation data while proceeding from right toleft across said row of digital elevation data.

Yet another aspect of the invention is directed to the aforementionedmethod wherein said digital elevation data is comprised of at least twovalues which differ in magnitude.

An additional aspect of the invention is directed to an image comprisinga plurality of pixels each of said pixels having an intensity of a firsthue and an intensity of an orthogonal second hue wherein when viewedwith apparatus which admits the first hue to a viewer's right eye andadmits the second hue to the viewer's left eye, the image is perceivedto be three-dimensional with each of said pixels projected as thoughviewed from directly above, with a uniform eye separation, and a uniformheight.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a cross section of digitalelevation data illustrative of the algorithm employed to create thethree-dimensional data projection.

FIG. 2 is a schematic cross-sectional view of a single row of digitalelevation data illustrative of the variables and parameters which definethe operation of the algorithm employed to create the three-dimensionaldata projection.

DETAILED DESCRIPTION

Creation of anaglyphs possessing the requisite properties detailedwithin require the following steps:

First, image data and digital elevation data are collected and convertedto digital form on a computer. If the image data is geographic innature, it is geo-referenced so that each image pixel possesses a uniquelatitude and longitude attribute. This geo-referenced image data maythen be projected in accordance with any desired geographic projection.Once projected, the image data is cropped into a rectangular formatcontaining an integer number of rows and columns. Pixels comprisingimage data derived from non-geographic sources including, but notlimited to, CAT scans, may be attributed by screen coordinates. Everypicture element, or pixel, comprising the image data can be uniquelyidentified by its row and column attribute. While a multitude ofconventions may be adopted for locating a pixel in the image data, onepreferred method which forms the basis for subsequent discussion hereinis to assign the upper-left most pixel the row/column designation (0,0).In an image comprised of x columns and y rows of data, the lowerright-most pixel is designated (y,x), the upper right-most pixel isdesignated (0,x), and the lower left-most pixel is designated (y,0).

In a similar manner, the digital elevation data corresponding to thearea covered by the image data is attributed such that each digitalelevation datum possesses a unique screen coordinate. To avoid thepresence of gaps in the final image, it is desirable that the image databe comprised of a number of pixels equal in magnitude to the number ofcolumns (x) multiplied by the number of rows (y). It is neithernecessary nor common for there to exist as many digital elevation valuesas there exist image pixels. Because digital elevation models typicallyconsist of elevation values sampled at discreet intervals, numerousimage pixels can and typically will reside between corresponding digitalelevation values.

The image is then converted to a gray image in which each pixel containsa value defining its intensity with each pixel being of identical hueand saturation. The number of levels utilized is dependent upon the byterepresentation of the computer used. For example, if a graphic format isused to store the final image which uses one byte per pixel, only 256combinations of red, green, and blue are available from the fileformat's look-up table. Because the image must ultimately contain twooverlaid similar images, one rendered in red, the other in cyan, thenumber of possible combinations of every possible level of red and cyanmust not exceed 256 (a one byte integer can represent the numbers0-255). Therefore, each image should be reduced to a gray image byassigning each pixel the intensity nearest to it on a scale of 1 to 256divided into 15 possible levels. With each pixel having one of 15possible levels, combinations involving 2 such pixels, as on the finalimage, can have at most 15 squared, or 225 final possible values. Thisnumber is well within the limit of 256. Two, three, or even four byterepresentations may utilize gray images which vastly enhanced precisionregarding the levels of gray corresponding the intensities of theoriginal image. One preferred method for defining the intensity of apixel in a color image so as to translate the color image into oneconsisting of intensities of gray is to adopt the standard methodologyincorporated in the JPEG compression algorithm. In addition, if themethod to be utilized to view the results of the projection algorithmarticulated herein is other than anaglyphic in nature, the image datamay be left in a format capable of representing a multitude of hues.

Next, two nearly identical images are created. The images respectivelyreplicate what the viewer would see through the right and the left eyesafter applying the projection algorithm described herein. While FIG. 2details the algorithm as it pertains to the creation of the imagerepresenting the right eye view (hereinafter the “right view”), it willthereafter be obvious to one skilled in the art how to apply thealgorithm so as to create the image representing the left eye view(hereinafter the “left view”). With reference to FIG. 2, the algorithmemployed to create the two images proceeds as follows. The first row ofelevation data is retrieved. As mentioned, each row of image datapreferably contains as many pixel values as there are columns in theimage. Because, for each row of digital elevation data there aretypically fewer digital elevation values than there are columns, digitalelevation values are typically spread out across the row with gapssignifying missing elevation data spanning the distances in between.Were each point of elevation to possess the same elevation value and belocated at the same elevation as the image plane (the plane representingthe medium upon which the final image is to be printed or displayed) aviewer viewing each point of digital elevation from directly above thepoint would perceive the point to rest in exact conformity with itslocation within the row of data. For instance, a digital elevation valuelocated twenty columns from the left-most edge of the image would appearto reside twenty pixels from the left-most edge of the image. As isevident from FIG. 2, when the digital elevation cross section 9 differsin elevation from that of the image plane 11, the perceived location 12of each digital elevation point 13 as viewed from the right eye 15 ofthe viewer is deflected by a distance d from its original position to anew location within the retrieved row of elevation data.

With respect to FIG. 2, the perceived deflection distance d is computedas follows. E represents the distance between the observer's eyes. Forconvenience, this value is set at 2.75 inches but may be any otherdesired value which approximates the desired viewer eye separation.One-half E, or e, is the distance between nadir 16 and the right eye 15.D represents the distance from the image plane 11 to the viewer's eyes15, 17. The difference in elevation between a digital elevation point 13and the image plane 11 is denoted by v. V₀ represents the elevation ofthe image plane 11. V equals the elevation of each digital elevationpoint 13 measured from where V equals 0, which for land on earth is meansea level, for water depth is mean high tide, and for non-geographicsubject matter is a chosen point of reference from which to measure theelevation of the digital elevation points 13. The deflection of thedigital elevation point 13 is denoted by d and is identical in magnitudefor both the right eye 15 and the left eye 17 with only the sign(direction) of the deflection being reversed. The vertical exaggerationof the digital elevation data is denoted by x. In order to compute d foreach digital elevation point 13, it is necessary to know the fourconstant values E, V₀, D, and x. As mentioned, E is set at 2.75 incheswhile V₀, D, and x are chosen so as to create a final image of desiredcharacteristics. For example, if a canyon is to be processed with anouter rim elevation of approximately 5,000 meters, V₀ may be set at5,000 meters so that the canyon will appear to recede behind the imageplane 11. Conversely, V₀ may be set to the approximate height of thebase of a range of mountains so that the mountains appear to rise out ofand in front of the image plane 11. D is typically set to a valuebetween twelve and twenty-four inches but may be set to any appropriatevalue conducive to the desired effect of three-dimensional relief.Lastly, the vertical exaggeration x is chosen to provide the desiredeffect of three-dimensional relief Often, it is advantageous toexaggerate the elevations of relatively flat digital elevation sets soas to enhance the resultant three-dimensional effect.

As the value V is known for each digital elevation point 13, the valueof d is readily computed. Because triangles A and B are similar righttriangles the following relationships must hold true:

d/v=e/(D−v)

and

d=ve/(D−v) where v=Vx−V ₀.

It is therefore possible to compute the deflection d for each digitalelevation point 13.

To illustrate the incorporation of the derivation of d into thealgorithm for producing the left and right views, reference is made toFIG. 1. Each pixel in the right view image is computed from the grayimage in the following manner. Moving down the gray image row by row,the corresponding digital elevation cross section 9 is retrieved.Depending upon the spacing of the digital elevation data, it is probablethat some rows of the digital elevation data will contain no datavalues. To generate the required points of data for each row, theoriginal grid of digital elevation points is interpolated in both the xand y directions as is necessary. While linear interpolation ispreferred, numerous interpolation techniques are known in the art. Asmentioned, because there are usually fewer elevation points per row thanimage pixels, multiple image pixels will be plotted between known pointsof elevation. Proceeding across the first row from left to right, theposition of each digital elevation point 1-7 is moved to the left or tothe right in the digital elevation data row according to its computeddeflection d. As previously detailed in FIG. 2, this displacement iscomputed by passing an imaginary ray from the right eye of the viewer,through the digital elevation point 1-7, and across the image plane 11.The rays' intersections with the image plane 11 determine the newlocations of the digital elevation points 1-7 along the correspondingright view image row denoted by 1′-7′ as shown in FIG. 1(b). Because thedigital elevation points 1′-7′ used to create the right view are derivedby ascertaining their corresponding digital elevation points 1-7 oforigin in the original retrieved row of digital elevation data, thealgorithm employed herein is said to be “backwards looking” in nature.As is evident from FIG. 1, digital elevation points 2,3,6,7 residingbelow the image plane are deflected to the right. Digital elevationpoints 4,5 residing above the image plane are deflected to the left.Note that digital elevation point 1 which rests at an elevation equal tothat of the image plane is not deflected at all.

Next, the portion of the corresponding image data row extending betweenany two consecutive points on the original row of digital elevation datais replotted on the corresponding row of the right view image utilizingthe displaced and deflected digital elevation points 1′-7′. For example,in FIG. 1(c), the original image pixels extending along the retrievedrow from point 1 to that of point 2 are stretched slightly to extendfrom 1′ to 2′ in the right view image row. This process continues from 2to 3, from 3 to 4, and so on. Note that portions of the original imageare overwritten in the new right view image as happens when the 4′ to 5′segment overwrites the 3′ to 4′ segment and part of the 2′ to 3′segment. This results from these sections being occluded when viewed in3-D. This process is repeated for every row. The left view image iscomputed in a similar manner for the left eye except the algorithm isemployed row by row with each row being computed by moving from right toleft.

Next, the two computed images are aligned and added together to form afinal anaglyph. If the final image is to be an anaglyph, the imageintensities comprising the right view image and the left view image areassigned orthogonal hues. Most preferred is to assign all pixels in theright view image an intensity of red and to assign all pixels in theleft view image an intensity of cyan (equal amounts blue and green).When the two images are aligned atop one another and the pixel valuesfor the final anaglyph are computed, the amount of red required at eachpixel in the final image is equal to the red value of the correspondingright view image pixel and the amount of cyan required at each pixel inthe final image is equal to the cyan value of the corresponding leftview image pixel. At this point, additional image data and DEMs may becombined to form other anaglyphs corresponding to the same area as thefinal image and the results may mixed with the first anaglyph at anydesired level of opacity. Many algorithms for combining images atvarying degrees of opacity will become obvious to one skilled in theart.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method of combining digital image data withdigital elevation data to produce two separate images said separateimages, when viewed one with the left eye and the other with the righteye, producing the sensation of binocular three-dimensionality,comprising the steps of: (a) combining said digital image data with saiddigital elevation data to compute a right eye view image with each pixelin said right eye view image corresponding to the pixel in said digitalimage data which would appear in three dimensions to reside at thelocation of said right eye view image pixel were each of said digitalimage data pixels to reside upon the surface defined by said digitalelevation data each of said pixels in said Tight eye view image computedfrom a vantage point directly above and unique to the correspondingpixel in the digital image data; (b) combining said digital image datawith said digital elevation data to compute a left eye view image witheach pixel in said left eye view image corresponding to the pixel insaid digital image data which would appear in three dimensions to resideat the location of said left eye view image pixel were each of saiddigital image data pixels to reside upon the surface defined by saiddigital elevation data each of said pixels in said left eye view imagecomputed from a vantage point directly above and unique to thecorresponding pixel in the digital image data; and (c) displaying saidleft eye view image and said right eye view image so as to produce thesensation of binocular three-dimensionality.
 2. The method of claim 1wherein each of said vantage points is located at a uniform height. 3.The method of claim 2, wherein said left eye view image and said righteye view image are not each comprised of a representation of every pixelin said digital image data arising from the effects of an occlusion whensaid digital image data is viewed in combination with said digitalelevation data.
 4. The method of claim 2, wherein the digital image datais preprocessed into a gray image each pixel-of which contains equalamounts of red, blue and green, said gray image being subsequentlycombined with said digital elevation data to create and display saidleft eye view image and said right eye view image.
 5. The method ofclaim 4, wherein an anaglyph is formed from said left eye view image andsaid right eye view image comprising: (i) assigning each pixel in saidleft eye view image a single hue; (ii) assigning each pixel in saidright eye view image a single hue which is orthogonal to said single hueassigned to each pixel in said left eye view image; and (iii) assigningeach pixel in said anaglyph the sum of the red, blue, and green valuespresent in each corresponding pixel from both the left eye view imageand the right eye view image.
 6. The method of claim 2, wherein saidleft eye view images and said right eye view images are displayed on asurface in a manner comprising continuously repeating in an alternatingfashion: displaying said left eye view image on the surface in a mannerso as to be perceivable by only the viewer's left eye; and displayingsaid right eye view image on the surface in rapid succession with saiddisplaying of said left eye view image in a manner so as to beperceivable by only the viewer's right eye.
 7. The method of claim 2,wherein each of said left eye view images is comprised of multipleseparate left eye view images and each of said right eye view images iscomprised of multiple separate right eye view images combined in amanner comprising the steps of: (a) computing multiple separate saidleft and right eye view images each covering an area which intersects inwhole or in part with that of at least one other separate said left orright view image; (b) assigning a multiplier between 0 and 1 to eachseparate said left or right eye view image corresponding to the desiredopacity of each separate said view image; (c) applying the correspondingmultiplier to each pixel of each of said separate view images; and (d)adding each corresponding pixel value from each separate left or rightview image to form one each of final said left and right eye viewimages.
 8. The method of claim 7, wherein each of said left and rightview images are perceived as consisting of multiple layers ofthree-dimensional images, each of said layers being partially, fully, ornot at all transparent with respect to other said layers ofthree-dimensional images.
 9. The method of claim 2, wherein each row ofthe right eye view image is created by projecting a single row of saiddigital image data in conjunction with a single row of said digitalelevation-data while proceeding from left to right across said row ofdigital elevation data.
 10. The method of claim 9, wherein each row ofthe left eye view image is created by projecting a single row of saiddigital image data in conjunction with a single row of said digitalelevation data while proceeding from right to left across said row ofdigital elevation data.
 11. The method of claim 2, wherein said digitalelevation data is comprised of at least two values which differ inmagnitude.
 12. An anaglyph of an image, said anaglyph comprising aplurality of a anaglyph pixels, each of said anaglyph pixels having anintensity of a first hue and an intensity of an orthogonal second huewherein: when viewed with apparatus which admits the first hue only to aviewer's right eye and admits the second hue only to the viewer's lefteye, the image is perceived to be three-dimensional with each pixel inthe image projected from an associated vantage point unique to suchpixel.
 13. The anaglyph of claim 12 wherein each said vantage point islocated directly above the associated pixel at a uniform height.
 14. Amethod for preparing an anaglyph as a combination of left and right eyeviews combining digital image data defining image pixels withcorresponding digital elevation data defining different elevationsassociated with respective ones of said image pixels, said left andright eye views when viewed with the left and right eyes, respectively,producing the sensation of binocular three-dimensionality, comprisingthe steps of: for each of a first plurality of said image pixels,computing a projected position in the left eye view, said projectedposition being computed based upon the associated elevation, a viewpoint directly above such pixel with a given eye separation, and a givenheight above an image plane; for each of a second plurality of saidimage pixels, at least partially coincident with said first plurality,computing a projected position in the right eye view, said projectedposition being computed based upon the associated elevation, a viewpoint directly above such pixel, said given eye separation, and saidgiven height above said image plane; and combining said left and righteye views to produce the anaglyph.
 15. The method of claim 14 furthercomprising: selecting said given height; and determining whether anypixels in said digital image data are subject to an occlusion.
 16. Aanaglyph being a composite of left and right eye views of an image of anarea having a plurality of different elevations, wherein: the left eyeview comprises, for each of a fast plurality of pixels of said image, aprojection of such pixel computed based upon an associated elevation, aview point directly above such pixel wit a given eye separation, and agiven height above an image plane; and the right eye view comprises, foreach of a second plurality of pixels of said image, at least partiallycoincident with said first plurality of pixels, a projection of suchpixel computed based upon an associated elevation, a view point directlyabove such pixel, said given eye separation, and said given height abovesaid image plane.